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[209.85.220.65]) by mx.google.com with SMTPS id t10sor6505354ljd.5.2019.03.26.07.52.01 for (Google Transport Security); Tue, 26 Mar 2019 07:52:01 -0700 (PDT) Received-SPF: pass (google.com: domain of urezki@gmail.com designates 209.85.220.65 as permitted sender) client-ip=209.85.220.65; Authentication-Results: mx.google.com; dkim=pass header.i=@gmail.com header.s=20161025 header.b=mtRExl5r; spf=pass (google.com: domain of urezki@gmail.com designates 209.85.220.65 as permitted sender) smtp.mailfrom=urezki@gmail.com; dmarc=pass (p=NONE sp=QUARANTINE dis=NONE) header.from=gmail.com DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=from:date:to:cc:subject:message-id:references:mime-version :content-disposition:in-reply-to:user-agent; bh=XI8nG9Dzmt5ShimcJLgUrFfOlr1UjZ/4vfezN58z7mI=; b=mtRExl5rQvp5nbXGCI/zHz/hSZxZNfiZyNqO8FojEpmtvcCqNgzb3mRjnpamZQpWW1 K+OA4pLUbXctnOw0xvAiKD02hDCUZfrUw71JcmXKz/mqRJCXsvCpSj/+3/KGT3+5+8eh r2sLoGsjsor9eNEnoOIzMKNlos+7JfVp57yi62KnmvFjoB/uNd9J/1yl7Q3y1rjPHEgO TuK1VMYuXbA09G7aFW3F0IZPrMpQru4ZFRCakwwB6slytwAsXVG9WwFVEVp8Y9F2Gb0k Yzf0P9fLan8AXDY5nSAb11qnf+GkkzITTpGXt+nGctYowVFX3P3Bkeq9oD3wYv3qymgD 7Uow== X-Google-Smtp-Source: APXvYqzTtQP+oFFD8jGFvpEJTrQjS1fwAFTra0tU4Xfa6gY3j2lgi5Z8Wwn4YaJfUT5HfAbn7DrrrQ== X-Received: by 2002:a2e:9655:: with SMTP id z21mr16910027ljh.60.1553611921190; Tue, 26 Mar 2019 07:52:01 -0700 (PDT) Received: from pc636 ([37.139.158.167]) by smtp.gmail.com with ESMTPSA id y1sm4118474ljj.13.2019.03.26.07.51.59 (version=TLS1_2 cipher=ECDHE-RSA-CHACHA20-POLY1305 bits=256/256); Tue, 26 Mar 2019 07:52:00 -0700 (PDT) From: Uladzislau Rezki X-Google-Original-From: Uladzislau Rezki Date: Tue, 26 Mar 2019 15:51:53 +0100 To: Uladzislau Rezki Cc: Roman Gushchin , Andrew Morton , Michal Hocko , Matthew Wilcox , "linux-mm@kvack.org" , LKML , Thomas Garnier , Oleksiy Avramchenko , Steven Rostedt , Joel Fernandes , Thomas Gleixner , Ingo Molnar , Tejun Heo Subject: Re: [RFC PATCH v2 1/1] mm/vmap: keep track of free blocks for vmap allocation Message-ID: <20190326145153.r7y3llwtvqsg4r2s@pc636> References: <20190321190327.11813-1-urezki@gmail.com> <20190321190327.11813-2-urezki@gmail.com> <20190322215413.GA15943@tower.DHCP.thefacebook.com> <20190325172010.q343626klaozjtg4@pc636> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190325172010.q343626klaozjtg4@pc636> User-Agent: NeoMutt/20170113 (1.7.2) X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: Hello, Roman. > > > > So, does it mean that this function always returns two following elements? > > Can't it return a single element using the return statement instead? > > The second one can be calculated as ->next? > > > Yes, they follow each other and if you return "prev" for example you can easily > refer to next. But you will need to access "next" anyway. I would rather keep > implementation, because it strictly clear what it return when you look at this > function. > > But if there are some objections and we can simplify, let's discuss :) > > > > + } > > > + } else { > > > + /* > > > + * The red-black tree where we try to find VA neighbors > > > + * before merging or inserting is empty, i.e. it means > > > + * there is no free vmap space. Normally it does not > > > + * happen but we handle this case anyway. > > > + */ > > > + *prev = *next = &free_vmap_area_list; > > > > And for example, return NULL in this case. > > > Then we will need to check in the __merge_or_add_vmap_area() that > next/prev are not NULL and not head. But i do not like current implementation > as well, since it is hardcoded to specific list head. > Like you said, it is more clever to return only one element, for example next. After that just simply access to the previous one. If nothing is found return NULL. static inline struct list_head * __get_va_next_sibling(struct rb_node *parent, struct rb_node **link) { struct list_head *list; if (likely(parent)) { list = &rb_entry(parent, struct vmap_area, rb_node)->list; return (&parent->rb_right == link ? list->next:list); } /* * The red-black tree where we try to find VA neighbors * before merging or inserting is empty, i.e. it means * there is no free vmap space. Normally it does not * happen but we handle this case anyway. */ return NULL; } ... static inline void __merge_or_add_vmap_area(struct vmap_area *va, struct rb_root *root, struct list_head *head) { ... /* * Get next node of VA to check if merging can be done. */ next = __get_va_next_sibling(parent, link); if (unlikely(next == NULL)) goto insert; ... } Agree with your point and comment. Thanks! -- Vlad Rezki